The invention relates to an apparatus for detecting whether microwave oven's door is open and closed, particularly to an apparatus compensating for a defective mechanical switch by using a photo-detecting sensor.
When the human body is exposed to microwaves generated by a microwave oven, the human body is seriously hurt. For example, fi a human eye is exposed to microwave, it can cause cataracts.
In order to minimize said danger generated by exposing a human body to microwaves, the conventional microwave oven uses a mechanical switch so that the range operates only when its door is completely closed so that microwaves do not leak.
However, because of mechanical abrasion due to extended use over a long period of time, the mechanical switch may possibly malfunction. Therefore, the microwave oven may operate with its door not completely closed, so that it is possible that microwaves leak out. In order to compensate for a defective mechanical switch, the opening and closing of the microwave oven's door is detected by a microprocessor; the self-contained microprocessor controls operation of the microwave oven according to a detected state, thereby leakage of microwave is protected.
As a typical example, U.S. Pat. No. 4,638,137 disclosed such an apparatus. In that apparatus, cooking time is input through a keyboard, and, if the microwave oven's door is closed, a door key pushes one part of a slide plate. A stop plate which is an integral part of a cooking start button prevents the slide plate from moving. However, if the cooking start button is pushed, the stop plate moves forward, so that the slide plate moves in the door key pushing direction and a heat start switch is closed. At this time, a first switch which connects first windings of a transformer to a power line is closed, and a second switch moving together with the first switch is closed, so that a signal informing that the heat start switch is closed is sent to a microprocessor. The microprocessor receives said signal and energizes relay windings via a converter, so as relay switch is closed and the first windings of the transformer are connected with the power lien. Also, power is applied to the first windings through a switch which moves together, with the door that is to say, when the door is closed, the switch is closed and, when the door is open, the switch is open, whereupon a magnetron operates and microwaves are generated.
Although a microprocessor is aware of the opening and closing of the door through the mechanical switch which detects the state of door and sends a signal corresponding to state of the door to the microprocessor, when the mechanical switch malfunctions, it is possible for the microprocessor to misunderstand the state of the door.